Azaleas would be lovely, but they would take a few years to do much... at least mine have. The look like they are going to bloom soon, though!! :) Knockout roses would be wonderful. I planted some last year and they have been going crazy ever since. I have found that if I go to the larger stores like Lowes, they will have plants that are from the area I love in and would have a better chance of not killing (not that I am speaking from experience....);). People from the local nursery could give you ideas, too. They would know if there were native plants that wouldn't make her allergies go crazy. Good luck and let us know what she picks!! :)

I agree on the choice of the knock out roses with maybe monkey grass to border the walks. The knockout rose also stay close to the ground and don't grow as straggly as regular rose bushes. Mine have really flourished this year. They also stayed very pretty during the winter. Good luck sister-in-law.

Hostas grow well in the shade and have really pretty foliage - no flowers though. I also like bleeding hearts - very pretty in the early spring.I'm with Kelly - Lowe's will have whatever grows in your area.